Methods for the fractionation and analysis of proteins are developed and applied to the purification of specific proteins for the study of their function and structure. Ion-exchange displacement (IED) chromatography is being developed for the fractionation of macromolecules and particles of biological interest, employing carboxymethyldextrans (CM-Ds) differing in number of charges per molecule as displacers. The procedure is particularly advantageous when large amounts of source material must be used to obtain sufficient amounts of a minor component, since the resolving power of the system can be focused on the narrow range of affinity represented by the protein of interest and its nearest neighbors. However, it is also applicable to ion-exchange HPLC. Recent efforts have been directed toward the simplification of the preparation of the displacers. Application of the method to the isolation of the myeloblast maturation factor (MMF) from guinea pig serum has shown that even unfractionated CM-Ds can be used to purify the factor. An exploration of the binding of serum proteins to several metal chelate and hydrophobic adsorbents indicates that chromatography on one or two of these before IED-chromatography can simplify the purification.